1. Field of the Invention
The present invention relates to a milling cutter having a indexable wiper cutter insert, in which easy and precise positioning of the wiper cutter insert is possible.
2. Prior Art
In general, a milling cutter for use in finishing workpieces has a wide and flat cutting edge, called a wiper cutting edge, for finishing at a front end of a cutter body. Particularly, a throwaway milling cutter (hereinafter referred to simply as "cutter") having an indexable wiper cutter insert (hereinafter referred to simply as "wiper tip") does not require sharpening of the cutting edge, so that the cutter body can be used over a relatively long service life. Therefore, the tool cost is lower, and this type of cutter is widely used.
With respect to this type of cutter, there is disclosed a cutter having cutting edges for ordinary cutting operations and having wiper cutting edges for finishing in Japanese Patent Laid-Open No. Sho 60-85816. In the cutter in Sho 60-85816, the ordinary cutting operation by the cutting edges and the finishing by the wiper cutting edges are performed concurrently.
FIGS. 14 and 15 show a conventional cutter such as in No. Sho 60-85816. The cutter in these figures comprises a cutter body 1 in the shape of a ring and having a rotational axis. A plurality of cutting edges 2 and at least one wiper cutting edge 3 are disposed at a radially outer surface of the cutter body 1. In the figures, only one wiper cutting edge 3 is shown.
In the cutter, a radially outer surface of the cutter body 1 is formed with chip pockets 4A, 4B by removing radially outwardly a part of the wall of the cutter body 1. Recesses 5A, 5B are formed at a trailing portion of the chip pockets 4a, 4b. Positioning pieces 6A, 6B are attached in the recesses 5A, 5B.
The positioning piece 6A is thrusted and fixed to the recess 5A by wedge 8 attached to the recess 5A. In contrast, the positioning piece 6B is fixed to the recess 5B only by a screw 9, so as to reduce the volume of the chip pocket 4B.
A tip 10A having a cutting edge 2 is removably mounted to a front end of the locating piece 6A, and a wiper tip 10B having a wiper cutting edge 3 is removably mounted to a front end of the positioning piece 6B.
The cutting edge 2 is located at a radially outer portion of the wiper cutting edge 3 in order to carry out finishing by the wiper cutting edge 3 immediately after the rough cutting by the cutting edge 2, so that the rough cutting and finishing can be performed concurrently.
In an ordinary cutter, the positions of the cutting edges are adjusted after changing the tips so that the edges are in the best positions to obtain a fine finished surface of the workpiece. Particularly, in a cutter having a wiper cutting edge, because remarkably high precision of the dimensions and fine roughness of the finished surface are required for the finished workpiece, positioning of a wiper cutting edge must be carried out by very small vertical movements of the wiper cutting tips i comparison with ordinary tips.
In a conventional cutter having a wiper cutting edge such as the above, positioning of the wiper cutting edge 3 is carried out in such way that the screw 9 is rotated to release the positioning piece 6B, and a spacing sheet (not shown) inserted between the bottom wall of the recess 5B and a lower face of the positioning piece 6B is changed with another piece having different thickness; alternatively, the spacing sheet is ground to reduce the thickness thereof.
However, in the former case, the fine positioning of the wiper cutting edge is impossible, and in the later case, positioning is very complicated.
In order to solve the above-mentioned problems, a positioning mechanism for a wiper cutting edge is disclosed in Japanese Patent Laid-Open No. Sho 60-186311, an example of which is shown in FIGS. 16 and 17. In this cutter, a radially outer surface of a cutter body 1 is formed with a chip pocket 16. A recess 14 is formed at a trailing portion of the chip pocket 16. A cartridge 13 is attached to the recess 14, and a wiper tip 10B having a wiper cutting edge 3 is removably attached at a front end of the cartridge 13. A wedge 8 is inserted in the rear side of the cartridge 13 and attached to the bottom wall of the recess 14 by a screw 7. In the cutter, the positioning of the wiper cutting edge 3 is carried out in such a way that the wedge 8 is pushed into the recess 14 by rotating the screw 7 so that the cartridge 13 is projected forward.
However, in the cutter, because the value of the movement of the wiper cutting edge 3 is large, fine positioning of the wiper cutting edge 3 cannot be performed.